The present invention relates to structure at the slice region of a headbox or the like of a paper or equivalent machine. In particular, the present invention relates to the structure for supporting and adjusting a strip which defines the upper lip of the slice.
With respect to the state of the art, reference may be made to applicant's Finnish Pat. No. 41342.
As is well known, a conventional headbox has a front wall beam situated at the upper lip region of the headbox slice and carrying the structure at the upper lip region of the slice. As a result any deformations or deflection of this front wall beam will undesirably influence the geometry of the slice inasmuch as such deformations or deflections are necessarily transmitted to the upper lip structure, and as a result there is also an undesirable influence on the transverse profile of the stream of paper stock which flows through the slice.
Of course, the above factors are well known. In the prior art, in order to reduce the extent of deformation or deflection of the front wall beam it is designed as an extremely robust member and is supported at points close to its Besselian points according to which, as is well known, any deflection due to the weight of the beam itself and due to its uniformly distributed load is minimized. Such deflections and deformations of the front wall beam are brought about not only by the weight of the beam itself but also as a result of the pressure load derived from the stock suspension which flows in the headbox and as a result of the temperature differential which exists between the exterior and interior of the front wall beam. It is recognized that this temperature differential is at a maximum during the starting-up operations of the paper machine.
According to known practice in the art, fine adjustment of the size and geometry of the slice is brought about by way of adjustment of an edge strip which defines the upper lip of the slice and which is normally fixed to the front wall of the headbox beam which is adjacent the slice in such a way as to be adjustable, suitable screws being provided for this purpose. The fine adjustment of such a strip which can be carried out according to known arrangements has a disadvantage in that the deflection of the beam which carries the strip which defines the upper lip, this deflection being at its most undesirable magnitude during the unstable starting operations, is for the most part transmitted to the structure which carries the fine adjusting mechanism, so that such undesirable deflection is necessarily transferred also to the strip which forms the upper lip of the slice.